Hot answers tagged

86

I am an EE system designer. I have designed many PC systems (and non PC ones). I do lots of power supply work and have dealt with many HDDs. As always, there is bound to be an exception somewhere. If someone told me to design an exception I certainly could, but here is my take: 30 seconds was always overkill in terms of any digital state. Even very ...


86

Hard drives have read/write heads which fly above the spinning disks when the drive is powered. When power is removed, the heads no longer fly... For a long time now, the arms which hold the heads have been designed to “auto-park” the heads away from the disks’ surface, or over a safe “landing zone”, when they lose power¹, but early (up to the mid 80s) hard ...


82

Bootable game disks do exist for the IBM PC. Conflict in Vietnam is an example of such a game. As can be seen on page 8 of the manual, the game boots directly without loading DOS first. The main reason it wasn't common was for compatibility. A self booting game has to have its own drivers for all the hardware it wants to support. As PCs quickly diversified ...


70

The original IBM PC and later variants used an Intel 8253 or 8254 as a sound chip. The 8253 is a timer circuit, containing three timers able to generate timed interrupts or square-wave output with programmed frequencies. On the PC the third timer's output is, via an amplifier, connected to a simple speaker. As said before, calling a 'simple' timer a sound ...


65

The Turbo button originally adjusted the clock speed of the computer between the full speed of the machine and a slower speed intended to be compatible with something more industry standard. It wasn't at all uncommon for software to be written with a specific speed of hardware in mind and either fail to operate completely or operate in a way that was ...


54

There was a 640K limit on the original IBM PC, but it was the result of IBM’s design decisions, and nothing to do with Microsoft: it’s the largest contiguous amount of memory which can be provided without eating into reserved areas of memory. The IBM PC Technical Reference includes a system memory map (page 2-25): which is detailed on subsequent pages: the ...


53

The reset button does not affect the power supply at all. It sends a reset signal to the CPU (and probably the bus). Some power supply designs indeed will wear quicker if quickly switched on and off, but this is not typically about still-charged capacitors. Depending on the circuitry, the following things among others could be a concern: Cumulative thermal ...


50

The 80s weren't homogeneous computing-wise. I'd break it down into roughly 3 eras: Early 80s: Atari, Commodore, Radio Shack, and Sinclair 8-bit machines (and their clones) were the most common in homes. For games consoles, Atari was king. Small businesses were using CP/M or Apple IIs (for Visicalc). Video is on dedicated CP/M systems. The Apple II was ...


45

The notion of a bootable-vs-non-bootable floppy is a little odd. It's worth noting that almost all floppies you're likely to have are actually bootable: it's just that they boot a program that isn't especially useful (it either displays a message saying to insert a system disk, or they execute INT 18h - which runs BASIC if it's installed in ROM, or displays ...


45

TL;DR: It was IBM's idea. IBM never intended to buy any of the software they acquired for the PC - and MS never intended to supply any OS beside Xenix. But MS (Paul Allen) soon recognized the potential business and acted accordingly. The Long Read IBM had no interest whatsoever in building up a basic software development for the PC. The strategy was ...


43

So you want to write a C program for the IBM PC before the first C compiler for the PC is released. How do you go about it? There are three options I can see: Write your own C compiler Use a cross compiler for 8086 on some other platform Wait for a C compiler to become available Don't use C No four options. Amongst our many options are fear, surprise and ...


40

I remember a conversation with an IBM engineer back in the 1980s, who implied there was an internal fight over this between IBM's engineering and marketing departments. The engineers wanted the PC to have the same keyboard as the popular 3270 mainframe terminal, for easy migration of users and software in a business environment, and in fact IBM did produce ...


38

The PC speaker connected to the i8253 PIT (programmable interval timer) was only for beeping. For better sound you need to bypass the PIT and use the Speaker as an I/O port with a single on/off bit controlled by the CPU. That way you can generate any sound (even PCM using a nasty PWM technique). The problem was that at that time the CPU was too slow, and ...


37

The Apple II was a hobbyist's computer that unexpectedly found a business niche. Apple recognised that niche in its design of 1980's Apple III. Specifically, it thought that the following were necessary changes to produce a business computer relative to the contemporaneous II+: a full-ASCII keyboard, with lowercase and uppercase entry; an 80-column display; ...


34

In general, yes, ISA cards have fixed memory and I/O addresses. ISA inherently has the card decide to what memory and I/O addresses it reacts because address decoders are located on the cards. How that decision is being taken varied over time, however. Because the ISA bus in principle exposes the full system bus to cards with no isolation or address ...


33

The first game sold for use on the IBM PC was Microsoft Adventure, which was available on the day the IBM PC was released (it was part of the launch, along with VisiCalc, Easywriter etc.). It was developed by Gordon Letwin (later of OS/2 fame) in 1979, based on the Colossal Cave mainframe game. It didn’t run on DOS though, it was a “booter” — you booted the ...


31

One option might have been using “Small C,” which was published in 1980 in Dr. Dobb's Journal magazine. Initially it generated code for the 8080, but was adapted for a few other CPU's. It was adapted to generate code for DOS/8088 but I do not know the date. Small C was written in itself so you would need a CP/M-80 system to do the port. But if I recall ...


30

Memory protection. It's not that preemptive multi-tasking is expensive, or hard. It's not. It's easy. It costs (or can cost) essentially the same as cooperative multitasking. You have to save process state in both cases. But what was holding back the older systems was their early reliance on systems without inherent memory protection, and those legacies ...


29

The BDS C compiler was released in 1979, ran on CP/M, and was capable of generating code for the Intel 8080 microprocessor. (It also ran on and generated code for the Zilog Z80, but that's not relevant here). This was a very popular, well-known CP/M compiler, and as Wikipedia says: It ran much faster and was more convenient to use than other Z80-hosted ...


28

According to Wikipedia, a number of reasons contributed to IBM’s using the 8088 instead of the 8086: Intel offered them a better price for the 8088 and was able to supply more of the chips; the 8-bit data-bus meant that IBM could use a modified 8085 design (the System/23) instead of coming up with a new 16-bit design; it also meant that IBM could use more ...


28

The 32-bit versions of Windows can still run many DOS binaries directly, using NTVDM, and VisiCalc stills works. VisiCalc was available at launch with the IBM PC, so is probably qualifies as the oldest commercial DOS program which can still run on modern versions of Windows without third-party software.


28

It was an advantage because the IBM PC became an extensible computing platform. The most popular competitor to it previously was the Apple II, another open platform. The PC, as a platform, was popular to users because of the choices it enabled, as developers because of the foundations that it laid, and engineering firms because they could focus on what they ...


27

One side of the cable is normally all ground. The other is all signals. This was done so a ribbon cable would have a ground wire between each signal wire, which helps prevent crosstalk. Flipping the cable swaps signals for grounds, grounding all signals. Since all the signals on a floppy disk are considered to be asserted when a zero (a logic 1 = ground) ...


24

What Boot Code? With 16 KiB it was pitched against the Apple II or the C64 with BASIC, nothing else. Remember that the PC (!) had a the cassette port? That's the intended mass storage for a 16 KiB system :)) The minimum requirement for floppy use was, as you already guessed, 32 KiB. And oh wonder, DOS can be booted on a 32 KiB machine. Still, not much space ...


24

Fundamentally, the lack of a specialized Programmable Sound Generator (PSG) or Synthesizer led to game sound effects and music on the IBM PC that were far inferior to competitors' microcomputers and game consoles. The comparatively inexpensive Commodore 64 had a PSG known as the SID that was capable of synthesized multi-track music, game sound effects, and ...


23

If you’re going for strict historical accuracy, a 1990 PC could have had either MS-DOS/PC-DOS 3.3, MS-DOS/PC-DOS 4.01, or DR DOS 5, along with Windows 3.0. MS-DOS 5 was released in 1991, and DR DOS 6 followed in the same year. An interesting OEM option is Compaq’s 3.31 DOS, which included support for partitions larger than 32MiB, and the first expanded ...


23

Here are a few innovations that are not attributable to IBM, but also are not attributable to PC clone manufacturers, either: LIM EMS, Lotus / Intel / Microsoft Expanded Memory Specification; IDE, designed by Western Digital (and later expanded into various ATA standards) ATX, designed by Intel USB, designed by a large number of companies including IBM and ...


23

Here's typical audio from a PC speaker: https://youtu.be/ZLwri0J1S4E As you can hear, it's really only designed to make beeps of various frequencies, all the same volume level. But by quickly turning the speaker on and off, you can play 1-bit PCM audio. Here's what it sounds like: https://youtu.be/HstgfH9FWV4 And because it's unbuffered, it's very CPU-...


23

Well there were some PC booter titles (MobyGames lists 249), but most of these were quite early games, even before hard drives, XMS or EMS even existed. These were almost always self contained single floppy games, that could run on the very specific hardware that existed. All they used was BIOS for disk access. Also DOS was not the only operating system, so ...


22

I think the answer is Lotus 1-2-3. Working in a spreadsheet, you are going to want to be able to use the numeric keypad for quick numeric entry, and you are going to need to use the cursor keys to move around the spreadsheet. Having to continually hit the Num Lock to switch between "modes" would be a pain. I have no actual evidence to back this up, other ...


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